Integrated non-destructive method and device for electrochemical energy system diagnostics

ABSTRACT

The present invention is an integrated method and apparatus for determining the quality of electrochemical energy storage devices, especially batteries. The invention is based on an integrated usage of electromagnetic and ultrasonic energy to probe of the interior volume of the battery. The first probe is carried out when the battery is at an initial charged state. After the first probe stage, a discharge of the battery being diagnosed is carried out until the test battery is at a small fixed test charge value. Signals from the eddy current probes allow determination of the continuity of the discharge current during the discharge process. After the discharge of the battery, the above described test sequence is repeated. 
     The resultant eddy current signal generated at the initial state of the battery and the gradients of the eddy current signal and of the ultrasonic signal versus the battery capacity is determined. Deviations of these parameters from the corresponding average values preliminary obtained on the training sample set of batteries is calculated. Probability density function binary signals are formed for deviations of parameters used. The batteries being diagnosed are rejected by means of using the obtained binary signals with their probability values and a logical rule set.

CROSS-REFERENCE TO RELATED APPLICATIONS

Claims priority of Provisional Patent Application No. 60/855,693, Filed Oct. 31, 2006

FEDERALLY SPONSORED RESEARCH

None

SEQUENCE LISTING

None

FIELD OF THE INVENTION

This invention relates to quality testing of batteries and the like, and specifically to the use of combined eddy current and ultrasonic methods and corresponding device for rapid determination of quality and charge state of batteries.

BACKGROUND

As batteries become more widely used as electrical power sources in a wide range of devices, the ability to determine the condition of a battery (including charge state) is of increasing value. Such is especially the case when the batteries are to be used in mission critical applications where they cannot be readily accessed or replaced and where battery failure would incur unusually high costs. Such applications are myriad and might include remotely located sensor equipment, satellites, smart weapons, medical and communications equipment and so forth.

The most common means of determining the condition and charge state of batteries at present is to monitor its electrical potential. This method is of limited value for batteries that have flat discharge curves, because battery voltage begins to drop only near the end of the discharge cycle, and thus cannot be reliably used to determine condition or amount of energy available during the current discharge cycle.

The present invention allows accurate determination of battery charge state, as well as the overall condition, and hence the reliability, of the battery.

BRIEF DESCRIPTION OF THE INVENTION

The integrated method and device of the present invention allows determination of battery quality. The present invention is based on the combined use of electromagnetic and ultrasonic excitation of the entire battery being tested. Analyses of eddy current and ultrasonic signals are used to probe the inner volume of the battery in the initial charged state.

After the first probing stage, a discharge of the battery being diagnosed is carried out to bring the battery to a small fixed test charge value (a specific fraction of full charge capacity). During this process the signals of the eddy current probes are used to determine the continuity of the discharge current. After the discharge process is finished, ultrasonic and eddy current testing of the battery is repeated.

The deviations of the eddy current signal obtained in the initial state of the battery being tested, and of the gradients of the eddy current and of the ultrasonic signals versus the battery capacitance, are determined relative to the average values preliminary obtained on the “training set” of batteries.

From the items of the training set, a defect subset is formed. The defect set includes the batteries subjected to an artificial discharge to a specific fraction of the initial capacity of the battery, with each part having a value that is proportional to its ordinal number in the defect set.

Using the batteries from the defect set, the functions for the probability density are determined for the deviations of the eddy current signal obtained in the initial state of the battery and of the gradients of the resulting ultrasonic and eddy current signals.

When the deviation values of the eddy current resultant signal obtained in the initial state of the battery, and of the gradients of the ultrasonic and of the eddy current resultant signals exceed the corresponding thresholds, separate binary signals are formed while each of these signals has a probability that is determined according to the corresponding probability density function.

The decision as to whether to reject the specific battery being tested is made using the obtained binary signals and logic rules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Block diagram showing the main components of the present invention.

FIG. 2. Diagram showing placement of the battery on the eddy current probe: 1—windings of the eddy current probe, 2 and 3 are cross section view of the battery case, 4 is the anode material, 5 is the separator with electrolyte, 6 is the cathode material.

FIG. 3. Frequency dependencies for batteries with T=5.4 mm in initial state.

FIG. 4. Dependencies of the difference of the reactance of the eddy current probe R_(r)=R_(ad)/ωL₀ normalized to the initial value of the R_(r) (Q_(r)=0) of the decreasing battery capacity: A₁, A₂, A₃ are the numbers of the batteries with T=5.4 mm. Dependencies are defined at a frequency of f=30 MHz.

FIG. 5. Dependence of the amplitude of the ultrasonic signal passed through a battery of thickness T=5.4 mm on the capacity when connected to a load. Markings A₁, A₂, A₃ are designated the numbers of batteries being tested.

FIG. 6. Dependence of voltage on terminals of the load resistor connected to the battery of thickness T=5.4 mm (A₁) on the discharge time in hours. The discharge was carried out at a current of I=15 mA, with a current density of j=126 mA/in².

FIG. 7. Dependence of voltage on terminals of the load resistor connected to a battery of thickness T=5.4 mm (A₂) on the discharge time in hours. The discharge was carried out at a current of I=15 mA, with a current density of j=126 mA/in².

FIG. 8. Dependence of voltage on terminals of the load resistor connected to a battery of thickness T=5.4 mm (A₃) on the discharge time in hours. The discharge was carried out at a current of I=15 mA, with a current density of j=126 mA/in².

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises an integrated method and device and for determining the quality of batteries. In practice, the method component of the invention comprises can be carried out as follows. The inner volume of a battery found in its initial charged state is probed with ultrasonic pulses in a high-frequency shadow fill mode by using ultrasonic probes containing polyurethane couplers (protectors) for ultrasonic energy injection. The inner volume of the battery found in its initial charged state is also probed with an eddy magnetic field by using eddy current probes spatially integrated with ultrasonic probes and arranged on both sides of a flat (prismatic) battery.

The battery being diagnosed is then discharged to a low fixed test charge value while using the signals of the eddy current probes for determining the continuity of the discharge current during the test discharge process. After the test discharge, the battery is probing with ultrasonic pulses, and the eddy current signals from the battery are determined using eddy current probes after the testing discharge, thus forming of a resultant eddy current signal.

The deviation of the resultant eddy current signal generated at the initial state of the battery being diagnosed from the average state of the same signal preliminary obtained on the training sample set of batteries. The plot of ultrasonic signal gradient versus the battery capacity is then determined as is the gradient of the resultant eddy current signal versus the battery capacity. Deviation of the ultrasonic signal gradient for the battery being diagnosed from the average gradient value preliminary obtained on the training sample of batteries is then determined, as is the deviation gradient of the resultant eddy current signal for the battery being diagnosed from the average gradient preliminary obtained on the training sample set of batteries.

A set of probability density functions for the deviations of the eddy current resultant signal obtained in the initial state of the battery, and the gradients of the ultrasonic and eddy current resultant signals; is then created.

This yields a binary signals for the deviations of the resulting eddy current signal obtained in the initial state of the battery, and the gradients of the ultrasonic and eddy current resultant signals while using the corresponding threshold for determining the probabilities of the obtained binary signals from the battery being diagnosed. Base on the resulting binary signal and associated logic rules, the battery being tested can either be accepted as of adequate quality or rejected.

A functional diagram of the device for battery quality diagnostic is shown in FIG. 1. The device comprises integrated measuring transducers arranged on both sides of a flat battery that correspondingly contain an emitting (or transmitting) and a receiving ultrasonic probes with polyurethane protectors, and parametric eddy current probes integrated with the ultrasonic probes into a single structure, as well as contacts for testing discharge of the batteries.

To the outer end face of the dielectric casing of each inductance coil, a thin metallic plate is affixed in the form of a split ring and having a current tap. The cylindrically shaped polyurethane protector protrudes above the level of the outer surface of the plate fixed to the end face of the dielectric casing.

The device of the present invention further comprises unit (designated as a circuit or block) for discharging of batteries that serves to connect of the discharge contacts to a resistive load during the specified time interval, as well as a generator for excitation of the ultrasonic probes. The device includes a measuring circuit for the ultrasonic probe, the first and the second measuring circuits for the eddy current probes, an analog-to-digital converter, a block (or circuit) for forming a resultant signal of the eddy current probes, a data storage unit, a means for determining the gradient of eddy current signal, a means for determining the gradient of ultrasonic signal, and a means for determining the deviations of the resultant signal of eddy current probes and the gradients of the eddy current and ultrasonic signals from the corresponding average values obtained on the training sample.

The device also includes a unit (circuit or block) for comparing with the thresholds and for forming the signals of binary logic, a means for forming the rejection signals, a means for determining the probabilities of the formed binary signals, and a means for rejecting batteries that are not of adequate quality according to the operation and logic rules of the device.

A detailed description of the invention is provided in terms of a specific application example. This example illustrates the results obtained on three silver-zinc batteries designated as A₁, A₂, and A₃. The diameter of the batteries is 10 mm, and battery thickness is 5.4 mm. Battery capacity is Q=150 ma·h. The batteries were studied using a probing magnetic field to produce eddy currents (FIG. 2) and an ultrasonic method.

Table 1 shows the results of analysis of the batteries in their initial charged state using an eddy current method.

Here f, is in MHz and is the frequency of the probing (excitation) eddy magnetic field. R_(ad) is the real part of the impedance introduced into the eddy current probe (reactance), ωL₀ is the self reactance of the probe, R^(r)=R_(ad)/ωL₀. The numeric index designates the number of battery.

Table 1 shows that the values R₂ ^(r) (for battery A₂) obtained at the initial state of the battery substantially exceed the values of the corresponding parameters for batteries A₁ and A₃ at all frequencies, while the values of these parameters for batteries A₁ and A₃ are approximately equal (FIG. 3).

TABLE 1 Eddy current method results from tests on batteries in their initial charged state. f, (R_(ad)/ (R_(ad)/ (R_(ad)/ (R^(r) ₂ − R^(r) ₃), (R^(r) ₁ − R^(r) ₃), MHz ωL₀, %)₁ ωL₀, %)₂ ωL₀, %)₃ % % 9 1.544 1.569 1.529 0.04 0.015 12 1.267 1.314 1.260 0.054 0.007 15 1.089 1.126 1.088 0.038 0.001 18 0.947 0.978 0.941 0.037 0.006 21 0.833 0.864 0.828 0.036 0.005 24 0.744 0.774 0.742 0.032 0.002 27 0.674 0.697 0.665 0.032 0.009 30 0.587 0.612 0.582 0.03 0.005

Then a test discharge was performed on batteries A₁, A₂, A₃ with a current of I=15 mA over a period of 6 minutes. The initial capacity of each battery was reduced in this case by 1%. After disconnection the battery from the load resistor, the charge of the battery is restored within a short time interval due to electrochemical processes in the battery (chemical power source).

Dependencies of the difference of relative reactance of the eddy current probe R_(r)=R_(ad)/ωL₀ normalized to the initial value of the R_(r) (Q_(r)=0) on the decreasing battery capacity: A₁, A₂, A₃ are the numbers of batteries with T=5.4 mm. Dependencies are defined at the frequency f=30 MHz (FIG. 4).

Following the test discharge, the eddy current and the ultrasonic measurements were repeated. The changes of parameter R₂ ^(r) in comparison to the initial state (gradient R₂ ^(r)) were as follows: for battery A₁; 0.12%, for battery A₃; 0.14%, for battery A₂; 0.40%. The corresponding changes of the ultrasonic signal amplitude compared to the initial state (amplitude gradient) were as follows: for battery A₁, the change was 0.35%, for battery A₃ it was 0.36%, and for battery A₂ is was 0.12%.

Dependences of the amplitude of the ultrasonic signal passed through a batteries of thickness T=5.4 mm on the capacity passed to a load are showed in FIG. 5.

Subsequent discharging of the batteries with current I=15 MA showed that the voltage on the current outlets of battery A₂ was maintained constant during 2 hours, while during the subsequent 2 hours it dropped to zero. In contrast to the above, the voltages on the current outlets of batteries A₁ and A₃ remained practically constant during 8 hours, whereupon an abrupt voltage drop began both on battery A₁ and battery A₃. Hence the battery A₂ is of low quality and has to be rejected. The value of the eddy current parameter R₂ ^(r) and the gradients of the eddy current and the ultrasonic signals for this battery substantially differ from the corresponding values obtained for batteries A₁ and A₃.

FIGS. 6, 7 and 8 show the dependences of voltage on terminals of the loading resistors connected to the battery of thickness T=5.4 mm (A₁), T=5.4 mm (A₂), T=5.4 mm (A₃) on the discharge time in hours. The discharge was carried out at a current of I=15 mA, with a current density of j=126 mA/in².

The method and device described here can be used for quality testing of other electrochemical devices comprised of current collectors, electrodes, electrolytes and an outer case or cover. The method and device of the present invention may be adapted to determine the quality of electric double layer capacitors of energy storage devices, for example.

CLOSURE

While various embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention. 

1. An integrated method for determining the quality of flat or prismatic batteries comprising the steps of: probing of the inner volume of a battery found in its initial charged state with ultrasonic pulses in a high-frequency shadow fill mode by using ultrasonic probes containing polyurethane protectors for ultrasonic energy injection; probing of the inner volume of a battery found in its initial charged state with an eddy magnetic field by using eddy current probes spatially integrated with ultrasonic probes and arranged on both sides of a flat battery; discharging the battery being diagnosed to a low fixed test charge value; using the signals of the eddy current probes for determining continuity of the discharge current during the test discharge process; repeated battery probing with ultrasonic pulses after the test discharge; determining the signals of the eddy current probes after the testing discharge; forming of a resultant eddy current signal; determining the deviation of the resultant eddy current signal generated at the initial state of the battery being diagnosed from the average state of the same signal preliminary obtained on the training sample of batteries; determining the ultrasonic signal gradient versus the battery capacity; determining the gradient of the resultant eddy current signal versus the battery capacity; determining the deviation of the ultrasonic signal gradient for the battery being diagnosed from the average gradient value preliminary obtained on the training sample of batteries; determining the deviation in the gradient of the resultant eddy current signal for the battery being diagnosed from the average gradient initially obtained on the training sample set of batteries; forming the probability density functions for the deviations of the eddy current resultant signal obtained in the initial state of the battery, and the gradients of the ultrasonic and eddy current resultant signals; forming of binary signals for the deviations of the eddy current resulting signal obtained in the initial state of the battery, and the gradients of the ultrasonic and eddy current resultant signals while using corresponding thresholds; determining the probabilities of the obtained binary signals for the battery being diagnosed using corresponding probability density functions; rejecting the batteries being diagnosed while using the obtained binary signals with their probability values and a logical rule set.
 2. Method according to claim 1, wherein the integrated measuring transducers arranged on both sides of a flat battery contain correspondingly an emitting and a receiving ultrasonic probes with polyurethane protectors, and parametric eddy current probes in the form of short cylindrical inductance coils, the dielectric casing of each inductance coil being coupled with the body of its respective ultrasonic probe and surround to the polyurethane protector.
 3. Method according to claim 2, wherein to the outer end face of the dielectric casing of each inductance coil, a thin metallic plate is fixed in the form of a split ring and having a current tap.
 4. Method according to claim 3, wherein the cylindrically shaped polyurethane protector protrudes above the level of the outer surface of the plate fixed to the end face of the dielectric casing.
 5. Method according to claims 1-4, wherein preliminary to the process of diagnostics a battery is placed on the polyurethane protector end face of the receiving ultrasonic probe, on the top thereof, while the end face of the polyurethane protector of the emitting ultrasonic probe is coaxially placed on the opposite surface of the flat battery, whereupon the probes are pressed to the battery body to the moment when the plates fixed to the end faces of the upper and lower eddy current probes come into contact with the battery body.
 6. Method according to claim 5, wherein the amplitudes of the ultrasonic pulses of the emitting ultrasonic probe are measured, said pulses having passed through the inner volume of the battery after the end of the process of pressing the emitting and the receiving probes to the battery body, and are subsequently used as signals of the ultrasonic probes.
 7. Method according to claim 2, wherein the real parts of the reactance of the lower and upper eddy current probes are measured that are compared to the self-reactance of each probe and are subsequently used as signals from the eddy current probes.
 8. Method according to claims 5 and 6, wherein the end of the process of pressing the emitting and the receiving ultrasonic probes to the battery body is determined according to the maximums of the real part of the reactance of the lower and upper eddy current probes.
 9. Method according to claim 1 and 3, wherein the testing discharge of the battery is carried out to a level not exceeding 1% of its capacity by connecting the current taps of the plates fixed to the end faces of the casings of the upper and lower eddy current probes to the specified resistive current load during the calculation time interval.
 10. Method according to claims 8 and 9, wherein the Fourier spectrum of the real component of the reactance of the lower and upper eddy current probes is determined during the battery test discharge process.
 11. Method according to claim 10, wherein the amplitude of the high frequency components of the spectrum is used to evaluate the contact stability of the plates fixed to the end faces of the casings of the upper and lower eddy current probes with the battery body.
 12. Method according to claim 1, wherein the signals of the lower and upper eddy current probes are determined after the test discharge and the resulting eddy current signal is formed by using the arithmetic averaging of these signals.
 13. Method according to claim 1, wherein from a batch of batteries of a given type a training set is formed containing not less than 20 batteries, by an random selection of batteries.
 14. Method according to claims 1 and 13, wherein the ultrasonic and eddy current signals are measured for each battery of the training set in their initial state and after the test discharge.
 15. Method according to claim 14, wherein the gradient of the ultrasonic signal is determined versus the capacity for each battery of the training set, as well as the average value of the gradient in the sample and the value of the root-mean-square error.
 16. Method according to claim 14, wherein the resultant eddy current signal is determined that is obtained in the initial state of the battery, and the gradient of the resultant eddy current signal for each battery of the training sample, as well as the average values of the resultant signal and of the gradient in the sample, and the value of the root-mean-square errors.
 17. Method according to claims 15 and 16, wherein batteries are selected from the training set for which the error value for the eddy current signal obtained at the initial state of the battery, or of each gradient exceeds 20%, and said batteries are excluded from the training set and the total quantity of the batteries in the set is subsequently increased to the nominal amount.
 18. Method according to claim 17, wherein from the items of the training sample set a defect subset is formed containing not less than 10 batteries.
 19. Method according to claims 18, wherein the defect subset includes the batteries subjected to an artificial discharge to a specific fraction of the initial capacity of the battery, with each said fraction having a value that is proportional to its ordinal number in the defect subset.
 20. Method according to claim 19, wherein, on the basis of the measurements performed on the batteries of the defect subset, the functions of the probability density are formed for the deviations of the eddy current resultant signal obtained in the initial state of the battery, and the gradients of the ultrasonic and of the eddy current resultant signals.
 21. Method according to claims 1 and 20, wherein when the deviation values of the eddy current resultant signal obtained in the initial state of the battery, and of the gradients of the ultrasonic and of the eddy current resultant signals exceed the corresponding thresholds, binary unit signals are formed while each of these signals has a probability that is determined according to the corresponding probability density function.
 22. Method according to claim 21, wherein the decisive logical rule for rejection includes an operation of integrating the eddy current resultant signal obtained in the initial state of the battery and the gradient of the eddy current resultant signal and of the coincidence of the integration result with the gradient of the ultrasonic signal.
 23. Method according to claims 21 and 22, wherein the rejection probability is determined using the probabilities of the obtained binary signals and of the said decisive logical rule.
 24. Device according to claim 1, comprised of: integrated measuring transducers arranged on both sides of a flat battery that correspondingly contain an emitting and a receiving ultrasonic probes with polyurethane protectors, and parametric eddy current probes integrated with the ultrasonic probes into a single structure, as well as contacts for testing discharge of the batteries; a circuit for test discharging of batteries that provides connecting of the discharge contacts to a resistive load during the specified time interval; a generator for excitation of the ultrasonic probes; a measuring circuit for the ultrasonic probe; the first and the second measuring circuits for the eddy current probes; an analog-to-digital converter; a block for forming a resultant signal of the eddy current probes; a storage unit; a means for determining the gradient of eddy current signal; a means for determining the gradient of ultrasonic signal; a means for determining the deviations of the resultant signal of eddy current probes and the gradients of the eddy current and ultrasonic signals from the corresponding average values obtained on the training sample; a block for comparing with the thresholds and for forming the signals of binary logic; a means for forming the rejection signals; a means for determining the probabilities of the formed binary signals; a means for rejecting the batteries.
 25. Device according to claim 24, wherein the polyurethane protectors of the emitting and the receiving ultrasonic probes have the form of cylinders of identical diameter and height that are glued to the operating end faces of the probes while the common axis of symmetry of each probe with the protector is preserved.
 26. Device according to claim 25, wherein the protectors are made using polyurethane with the Shore hardness of 16-20 units, and are glued to the operating end faces of the probes with a polyurethane glue that provides an acoustic transparency at the boundary of protector-operating surface of the probe.
 27. Device according to claim 24, wherein to the outer surface of each of the ultrasonic probes a thin-wall cylindrically shaped dielectric casing is fixed that co-axially embraces the polyurethane protector with a small installation clearance between the outer surface of the protector and the inner surface of the dielectric casing.
 28. Device according to claim 27, wherein to the outer end face of the dielectric casing a thin metallic plate is glued in the form a split ring, while the width of the plate is equal to the wall thickness of the dielectric casing, with the thickness not exceeding 0.5 mm.
 29. Device according to claim 28, wherein to the plates of the integrated measuring transducers arranged on both sides of the flat battery metallic current taps are fixed that are connected to the resistive load during the specified time interval.
 30. Device according to claims 25 and 27, wherein the polyurethane protector protrudes beyond the level of the outer surface of the plate by a value not more than 1 mm.
 31. Device according to claim 24, wherein to the inlet of the analog-to-digital converter the outlets of the first and the second measuring circuits of the eddy current probes are connected, as is the measuring circuit of the ultrasonic probes.
 32. Device according to claim 24, wherein the outlet of the circuit or block for testing discharge of batteries is connected to the input of the storage unit.
 33. Device according to claim 24, wherein to the input of the block or circuits for comparing the thresholds and forming the signals of binary logic are connected the outputs of the block for forming the resultant signal of the eddy current probes and of the blocks for determining the gradients of the eddy current signal and of the ultrasonic signal.
 34. Device according to claim 24, wherein the outputs of the blocks for forming the resultant signal of the eddy current probes and of the blocks for determining the gradients of the eddy current signal and the ultrasonic signal are connected to the input of the block for determining the deviations of the signals received from the corresponding average values of the training sample set.
 35. Device according to claim 24, wherein the outputs of the blocks for comparing with thresholds and forming of binary logic signals are connected to the inputs of the means for determining the rejection signal.
 36. Device according to claims 24 and 34, wherein the inputs of the means for determining the probabilities of the formed binary signals are connected to the outputs of the block for determining the deviations of the signals obtained from the corresponding average values on the training sample set.
 37. Device according to claims 35 and 36, wherein the inputs of the means for rejecting batteries are connected to the outputs of the means for forming the reject signal and of the means for determining the probabilities of the formed binary signals. 